Many intracellular processes are carried out or regulated by multi-subunit protein complexes that become active or repressed by the association or dissociation of individual polypeptide subunits.
One such group or family of proteins is related to the B subunit of transducin. Members of this group are all at least somewhat homologous to the .beta.-subunit of transducin at the amino acid level, and contain a varying number of repeats of a particular motif identified in .beta.-transducin. The repeats have been termed ".beta.-transducin", or "WD-40" repeats (Fong, et al.).
Among the members of this protein family (Duronio, et al.) are the G.beta. subunits that couple many receptors to their intracellular effector molecules, G.beta./.gamma. subunits that anchor another protein kinase (the .beta.-adrenergic receptor kinase, .beta.ARK), DNA binding proteins and yeast cell cycle proteins. All of these require a transient protein-protein interaction for their function. However, the sequences at the interface of these proteins and their partners have not been identified.